In the manufacture of semiconductor devices, metal vias and contacts are deposited into via openings and contact holes on semi-conducting wafers that have been preprocessed. Semiconductor devices are thus formed connected to each other by the metal vias and contacts to form an integrated circuit. In particular, aluminum, aluminum alloys, tungsten and tungsten alloys are frequently used for deposition into the via openings and contact holes on the semi-conducting substrate. These deposition processes can be carried out by a physical vapor deposition (or sputtering) or a chemical vapor deposition technique.
As semiconductor devices are continuously being made smaller in a total miniaturization effort for achieving devices on the sub-path-micron scale, the via openings and the contact holes must also be made smaller. Consequently, the openings and the holes to be filled have higher aspect ratios, i.e., the depth of the opening or hole divided by its diameter becomes higher.
Difficulties are encountered in depositing a conductive metal into via openings and contact holes by conventional sputtering processes when such openings or holes have high aspect ratios. As the openings and holes become smaller and deeper, the bottom and sides of an opening or hole receive fewer deposited metal particles then the top surface of the device. The end result of such a phenomenon, sometimes called shadowing effect, is that the metal layers formed by the particles hangs over the opening forming an overhang. Such overhang closes before the opening is filled as the deposition process progresses and thus creating a void in the opening or hole.
One technique that has been used to compensate for the shadowing effect of the sputtering process is to taper the sidewalls of the via openings or the contact holes. For instance, during the formation, i.e., by a dry etching or reactive ion etching process, the top of the opening or hole is etched more than the bottom of the opening or hole. The sidewalls of the opening therefore may have an inclined of 15.degree. with the vertical axis that is parallel with the length of the opening. The tapered via opening or contact hole correct significantly the under-fill or shadowing effect of the sputtering process, for instance, by aluminum particles. However, the tapered via or contact formed after fill by aluminum and then etched back, have the drawback of popping out of the via opening or contact hole or fails in a defect known as via delamination. The via delamination defect can be severe in a semiconductor device since the device, after formation of the via or contact, may be subjected to various thermal cycling processes encountered in various etching, passivation or planarization processes. The expansion or contraction of the metal via or contact caused by such thermal stress during cycling can easily delaminate the via or contact from its opening or hole. When the via delamination defect occurs, the circuit in the semiconductor device fails and thus the yield of the semiconductor wafer is significantly affected.
It is therefore an object of the present invention to provide a method of filling via openings and contact holes that does not have the drawbacks and shortcomings of the conventional methods.
It is another object of the present invention to provide a method for filling openings and contact holes that are slightly tapered with the top opening larger than the bottom opening by built-in anchors in the sidewalls of the via or contact.
It is a further object of the present invention to provide a method for filling via openings or contact holes by providing anchors on the via or contact in-situ as an integral part of the process recipe.
It is still another object of the present invention to provide a method for filling via openings and contact holes with a conductive metal such that the via and the contact subsequently formed does not have a delamination problem.
It is still another object of the present invention to provide a method for filling via openings or contact holes by a conductive metal by utilizing a deep UV photoresist which contains a photo-acid-generator.
It is yet another object of the present invention to provide a method for filling via openings and contact holes with a conductive metal by coating the sidewalls of the openings or holes with a flooring and hydrogen containing organic compound formed from the deep UV photoresist such that anchors can be etched onto the opening.
It is still another further object of the present invention to provide a method for forming vias or contacts in alternating layers of BPTEOS oxide and TEOS oxide by forming toroidal-shaped cavities at the interfaces between layers of different materials.
It is yet another further object of the present invention to provide a method for forming vias and contacts on a semiconductor device by using a deep UV photoresist and subjecting such photoresist to UV radiation such that the sidewalls of the via opening or hole can be etched into cavities for forming anchors on the via or contact.